It is the study of the brains and minds of ancient hominids, dating back to 7 million years ago. Newsweek reporter Sharon Begley gives a credulous tour of the standard Darwinist speculations: we can tell when humans first started wearing clothing by genetic analysis of modern body lice, or perhaps human society was the result of the emergence of the gene for oxytocin, a hormone that causes mothers to secrete milk and that may influence social behavior in humans.
Evolutionary paleoneurologists claim to know some of what ancient hominids actually thought by studying fragments of their fossilized skulls. I do research on living brains. My specialty is studying the pulsations in the blood flow that goes through the brain and trying to understand how the brain responds to the pulsations. I study rats and dogs in the laboratory, and I study brain blood flow in people using MRI scans. Tilly had many private tutors before attending Schiller-Schule, the only secondary school for girls in Frankfurt at that time.
Tilly Edinger continued her schooling with university studies in zoology , geology , and paleontology. While preparing her doctoral dissertation, Edinger encountered a natural brain endocast of Nothosaurus , a marine reptile from the Mesozoic era. Edinger's first paper, published in , centered on the characteristics of the Nothosaurus specimen.
Prior to the publication of her work, inferences about the evolution of the vertebrate brain were made exclusively through comparative anatomy of extant fish, amphibian, reptile, bird, and mammal brains. Tilly Edinger's background in neurology and paleontology paved the way for her to integrate comparative anatomy and stratigraphic sequence , thus introducing the concept of time to neurology and creating the field of paleoneurobiology.
The field was formally defined with the publication of Die fossilen Gehirne Fossil Brains in which compiled knowledge on the subject that had previously been scattered in a wide variety of journals and treated as isolated events. While still in Germany, Edinger began studying extant species from a paleoneurobiological perspective by making inferences about evolutionary brain development in seacows using stratigraphic and comparative anatomical evidence.
Edinger continued her research in Nazi Germany until the night of November 9, when thousands of Jews were killed or imprisoned in what became known as Kristallnacht. Although a visa was not immediately available for immigration to the United States, with the help of friends and colleagues who valued her work, Edinger was able to immigrate to London where she translated German medical texts into English.
Eventually her visa quota number was called and she was able to immigrate to the United States where she took on a position as a research fellow at Harvard's Museum of Comparative Zoology. Her contributions to the field of paleoneurobiology include determining the extent to which endocasts reflect the anatomy of ancient brains, the adequacy of comparative anatomy to interpret brain evolution, the ability of brain endocasts to predict the lifestyles of extinct organisms, and if brain size has increased over geological time; topics which are still being explored today.
In her later years, Edinger corresponded with the next generation of paleoneurobiologists, which insured that the work from her year career continued into the future. The pinnacle accomplishment of her career was the compilation of an annotated bibliography of paleoneurobiological papers published between and The bibliography, Paleoneurology , was completed and published by colleagues posthumously in due to the untimely death of Edinger from injuries sustained during a traffic accident in Paleoneurobiologists Ralph L. Holloway and Dean Falk disagree about the interpretation of a depression on the Australopithecus afarensis AL endocast.
Holloway argues that the depression is a result of lipping at the lambdoid suture and that the sulcal patterns indicate cerebral organization moving toward a more human pattern, while Falk insists that the depression is the lunate sulcus in a position that is indicative of an ape-like sulcal pattern. The debate between these two scientists is not hinged solely on the AL endocast, but rather extends to all australopithecine fossils, with Holloway insisting on the presence of hominid sulcal features, and Falk maintaining that the features are pongid in nature.
The debate between Holloway and Falk is so intense that between and , they published four papers on the identification of the medial end of the lunate sulcus of the Taung endocast Australopithecus africanus , which only further strengthened the division between each scientist's respective opinion. Although there have been no definitive conclusions about the fossils in question, many techniques were created or critically analyzed and refined as a result of the conflict.
These new techniques in endocast analysis included the use of stereoplotting to transfer sulci between differently shaped endocasts, measurement of indexes from photographs rather than directly from specimens, and confounding of measurements taken directly from specimens and those taken from photographs.
A brain endocast is the imprintation of the inner features of a cranium that captures the details created from pressure exerted on the skull by the brain itself. Endocasts can be formed naturally by sedimentation through the cranial foramina which becomes rock-hard due to calcium deposition over time, or artificially by creating a mold from silicon or latex that is then filled with plaster-of-Paris while sitting in a water bath to equalize forces and retain the original shape.
Natural endocasts are very rare; most of those that are studied are the result of artificial methods. Although the name implies that it is a copy of the once living brain, endocasts rarely exhibit convolutions due to buffering by the pia mater , arachnoid mater , and dura mater that once surrounded and protected the brain tissue.
Furthermore, not all endocasts are created from a complete cranial fossil and subsequently, the missing parts are approximated based on similar fossils. In some cases, fragments from several fossils of the same species are used to construct a single endocast.
More recently, computed tomography has played a large role in reconstructing endocasts. The procedure is non-invasive and has the advantage of being able to analyze a fossil in record time with little risk of damaging the fossil under review. CT imaging is achieved through the application of x-rays to produce tomographs , or sectional density images, which are similar to the images produced during MRI scans. Because the cranium and its contents are of different densities, the endocranial cavity and its unique traits can be reconstructed virtually. Radiographic technique such as computed tomographic imaging, or CT scans , coupled with computer programming have been used to analyze brain endocasts from as early as Vannier and G.
Conroy of Washington University School of Medicine have developed a system that images and analyzes surface morphologies in 3D. Scientists are able to encode surface landmarks that allows them to analyze sulcal length, cortical asymmetries and volume. Paleoneurobiology revolves around the analysis of endocasts. Much of this analysis is focused on interpreting sulcal patterns , which is difficult because traces are often hardly recognizable, and there are no clear landmarks to use as reference points.
Furthermore, the only clear reference plane is the sagittal plane one, which is marked by distinct cerebral asymmetries. Since the obtaining of clear data from fossil details is usually very difficult, much debate arises over interpretations. Experience is often an important factor in endocast analysis. Statistical analysis of brain endocasts gives information on the increases in overall brain volume "endocranial volume". Because endocasts are not exact replicas, or exact casts, of a once-living brain, computer algorithms and CT scans are needed to calculate endocranial volume.
The calculated endocranial volume includes the meninges , cerebrospinal fluid , and cranial nerves. Therefore, these volumes end up larger than the once-living brain. The corresponding body weight of the subject must also be known to calculated RBS. RBS is calculated by dividing the weight of the brain by body weight. EQ can be determined several different ways depending on the data set used. For example, Holloway and Post calculate EQ by the following equation:. Brain volume is prominent in the scientific literature for discussing taxonomic identification , behavioral complexity, intelligence, and dissimilar rates of evolution.
In modern humans, cranial capacity can vary by as much as cc, without any correlation to behavior. This degree of variation is almost equivalent to the total increase in volume from australopithecine fossils to modern humans, and brings into question the validity of relying on cranial capacity as a measurement of sophistication.
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Many paleoneurobiologists measure cranial capacity via the submersion method, in which displacement of water in a beaker is taken as the volume of the endocast. Scientists who believe that this method is not accurate enough will use a similar procedure in which a beaker with a spout is filled until it is full.
The water displaced by the endocast is then weighed to determine the endocast volume. Although both of these techniques are significantly more precise than previous methods, scientists are optimistic that more advanced techniques such as computed tomography will provide greater accuracy of volume measurements.
Morphometric analysis relies on chord and arc measurements of the endocast surface. Length, width, bregma - basion , and height measurements of an endocast are taken with spreading calipers. Measurements may be skewed if the orientation of the endocast has not been properly determined before the dioptograph is made.
Geometric morphometrics systems of coordinates superimposed over the measurements of the endocast are often applied to allow comparison between specimens of varying size. Convolutions, the individual gyri and sulci that compose the folds of the brain, are the most difficult aspect of an endocast to accurately assess. The surface of the brain is often referred to as smooth and fuzzy, due to the meninges and vasculature that cover the brain's surface.
It is possible to observe underlying gyri and sulci patterns if an endocast is accurately or preserved, but the uncertainty associated with these patterns often leads to controversy.
Paleoneurobiology - Wikipedia
The degree of asymmetry between right and left hemispheres is a point of interest to most paleoneurobiologists because it could be linked to handedness or language development of the specimen. Asymmetries occur due to hemispherical specialization and are observed in both a qualitative and quantitative manner. For example, a right-handed person typically has larger left occipital lobe and right frontal lobes than the contralateral lobes. Petalias also occur due to specialization in the communication centers of the frontal cortex of the brain in modern humans.
Petalias in the occipital lobe are easier to detect than those in the frontal lobe. Scientists use the presence of petalias to show sophistication, but they are not a definitive indicator of evolution toward a more human brain. Although the meninges have no link to behavior, they are still studied within the realm of paleoneurobiology due to the high degree of conservation of meningeal patterns within a species which may serve as a way to determine taxonomy and phylogeny. Because meningeal blood vessels comprise part of the outermost layer of the brain, they often leave vascular grooves in the cranial cavity that are captured in endocasts.
Endocranial vasculature originates around the foramina in the skull and in a living body would supply blood to the calvaria and dura mater. The vasculature is so well preserved in some fossils that terminal branches of the circulatory system can be observed.
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Analysis of cranial vasculature concentrates on the anterior meningeal system of the frontal region, the middle meningeal system of the parieto-temporal and part of the anterior occipital region, and the cerebellar fossa system of the cerebellar region. In the course of hominid evolution, the middle meningeal system has undergone the most change. Although cranial vasculature has been exhaustively studied in the last century, there has been no consensus on an identification scheme for the branches and patterns of the vascular system resulting from little overlap of results between studies.
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As such, endocranial vasculature is better suited for inferring the amount of blood delivered to different parts of the brain. It is impossible to determine accurate location of the central or precentral sulci from an endocast. Still it can provide a rough idea of lobe sizes.